|Title of Invention||
"PROCESS FOR PRODUCTION OF IRON ORE PELLETS"
|Abstract||The present invention concerns a process for production of iron ore pellets comprising at least one iron ore crushing stage in a roller press for the production of iron ore pellets. The crushing stage (s) can be done prior or after grinding, or still defined by successive passages of the material through the foregoing crushing stage.|
|Full Text||FIELD OF THE INVENTION
The present invention relates to a process for iron ore pellets and more specifically to a process in which an equipment for reducing the size of the solid iron ore particles is used.
BACKGROUND OF THE INVENTION
As it is known, peiletizing is an agglomeration process whereby the fine iron ore particles are converted into spherical bodies with size ranging from 8 to 18 mm. These spherical bodies having an appropriate physical, chemical and metallurgical properties for use in steel mill's reduction reactors.
The quality of the product yielded by the peiletizing process has direct relation with the material size fed to the process, and it is suitable that at least 50% of the raw material charged to the process have a size less than 0.40 mm (325 mesh) ,and a specific surface of 1200 cm2/g. Usually, the ore fines employed in pelleting have a granulometry 100% less than 0.149 mm (100 mesh), however only 30 to 45% being less than 0.044 mm (325 mesh Therefore, in order to adapt the granulometric characteristics and specific surface of the ore fines to the pelleting process requirements it becomes necessary to submit the ore fines to a crushing stage to reduce the particles size.
In the conventional pelletizing process the reducing of size (crushing and grinding) of the ore fines is achieved by grinding in a tubular mill wherein steel balls or truncated steel cones (cylpebs) are usually employed to help with the grinding operation or as a grinding medium. This grinding operation is a heavy burden on the overall production cost of pellets due to the significant consumption of energy and grinding media.
There are several options available to the grinding operation. It can be performed in or wet or dry, open or closed operations.
In the wet grinding process iron ore and water are mixed together and both are added to the mill in adjusted proportions performing a diluted grounded ore pulp. A large amount of water that is added to the grinding operation is removed by subsequent thickening, homogenizing and filtering stages.
On the other hand, dry grinding operation requires the prior drying of the ore fines, however disregards the water draining step that is necessary when the wet process is employed.
Grinding in an open operation consists in passing the material through the mill only once, while in the closed operation the hydrocyclones employed for wet grinding or the air classifiers used in the dry grinding process perform the granulometric classification at the discharge of the mill.
Finally, in the closed mills a fraction of sufficiently fine material below 0.44 mm (325 mesh goes on to the next stages of the pelletizing process while
the coarser fraction returns to the mill as the circulating load of the grinding process.
SUMMARY OF THE INVENTION
Some years ago, a new crushing technique was tested by the ore mining processing industry. The technology is based on the employment of high pressure to obtain the reduction in the ore particles size. The principle of high pressure crushing was introduced to industrial applications through the machine called roller press in which high pressures, above 50 MPa is applied to two rollers unto which is fed the material to be crushed.
In a roller press the crushing and grinding is achieved through the transfer of pressure between the particles of a bed or layer of material without using any external means of action, such as grinding elements, or coatings in the mill onto the individual particles of the material to be ground. Due to the high pressure as applied, the material which has been processed in a roller press is compacted into a shape of agglomerates called flocks.
Industrial roller presses, such as those which are employed by the cement industry, copper and diamond mines among others, are usually designed with rollers of 1.6 meters in width and 1.4 to 2.2 meters of diameter.
The peripheral velocity of the rollers is from 0.7 to 2.0 m/s and the hydraulic
power applied to the rolls ranges of 100 kN per linear roller centimeter, or
meters of diameter. The capacity of an industrial roller press may attain up
to 1000 tons/h, depending on the dimensions of the equipment, operating
conditions and the specific characteristics of the material to be crushed.
The main advantage of the roller press over conventional crushing equipment, such as ball mills and rock crushers are: a significant reduction in electric power of approximately 20 to 30% due to the ereater efficiency of energy transfer from the rollers surface to the particles at the beginning and afterwards between the particles; a significant Reduction in the operating cost due to (i) the elimination of grinding devices replacement, (ii) preventing fissures and cracks on the ore particles, (iii) consequently reduction of electric power needed for the subsequent stages of comminution, (iv) and the promotion of a greater degree of reactivity of the ore, specially during the interaction with liquids, for example in the leaching process of gold, and the interaction with gases as in the combustion process of coal or in the reduction of ores. Therefore, this provides for.a low costs of investment and the improvement of maintenance.
BRIEF DESCRIPTION OF THE accompanying/ DRAWINGS
The present invention will be described in accordance with the attached drawings which are not to be considered as limitations of the present invention.
Figure 1 is a schematic viewing of the conventional grinding process of iron ore fines carried out in a ball mill.
Figure 2 is a schematic viewing of a process for the iron ore pellets production, comprising a pre-comminution of the iron ore fines in a roller
Figure 3 schematically represents, a process for the iron ore pellets production comprising the post-comminution of the ore fines in a roller press.
Figures 4 and 4a, schematically represent two arrangements for a process for the iron ore pellets production with the total comminution of the fines in a roller press.
Figure 5 represents a block diagram of the stages in the production process of iron ore pellets having crushing stage prior to the wet grinding in the ball mill.
Figure 6 represents a block diagram of the stages in the production process of iron ore pellets having crushing stage prior to the dry grinding in the ball mill.
Figure 7 represents a block diagram of the stages in the production process of iron ore pellets in which the crushing stage is performed after the wet grinding in the ball mill.
Figure 8 represents a block diagram of the stages in the production process of iron ore pellets in which the crushing stage is performed after the dry grinding in the ball mill.
Figure 9 represents a block diagram of the stages in the production process of iron ore pellets having a series of crushing stage with a total comminution.
DETAILED DESCRIPTION OF THE INVENTION
According to the Figures above-cited, the present invention comprises a process for the iron ore pellets production in which the pellets are obtained in a roller press equipment.
Specifically the Figure 1 shows the raw material feeding 1 to be pelletized having a high specific surface of about from 450 cm /g to 1800 cm /g which is not dependent from the particularities of the conventional iron ore production process, being it carried out through a dry or wet, open or closed circuit.
The Figure 2 illustrates an iron ore pellets production process wherein the raw material feeding 1 for pelletizing is done in a roller press. The material is submitted to a pre-comminution 5 before the pelleting and after that it is immediately submitted to the other stages of conventional grinding in ball mills 2, 3, 4 or 2a, and 4a. According to this arrangement, the feeding 1 for the ore fines to be transformed in pellets is submitted to a single pass through the roller press 5 resulting in the increase of the specific surface from approximately 450 cm /g to about 1800 cm2/g. Then the material is crushed and fed into the conventional wet circuit of the ball mill 2a and 4a, or the dry 2, 3 and 4, where the specific surface is increased approximately to 1800 cm2/g.
The Figure 3 represents an iron ore pellet production process in which the comminution stage 5 of the pelletizing material is performed by crushing the material after the conventional grinding in the ball mills 2, 3, 4 or 2a and 4a. In this case, the iron ore fines feeding 1 has a high specific surface of approximately 450 cm2/g in the conventional wet grinding mill 2a and 4a or the dry 2, 3, and 4.
In the case of wet grinding 2a and 4a, the ground product is submitted to thickening stages 6, homogenizing 7 and filtering 8. Following the filtered material is crushed in the roller press 5 only once until the specific surface reaches 1800 cm /g. However, in the case of dry grinding 2, 3 and 4, the ground product with a specific surface of 1400 cm2/g is submitted to one single passage through the roller press 5 leading to a material with a specific surface of approximately 1800 cm2/g. This arrangement initially implies in the production of a coarser ground material 1 in comparison with the conventional process, since a supplementary comminution shall occur from the processing of this pre-molded material in the roller press 5.
Figure 4 represents the total comminution of the material to be pelletized wherein the ore fines feeding 1 has the specific surface raised from approximately 450 cm /g to about 1800 cm /g by the successive passages through the roller presses 5, 5a,....,5n. In this arrangement, the conventional wet or dry grinding process 2, 3 and 4, or 2a and 4a in ball mills is completely substituted by a process with "n" roller presses in series 6, 5a,...,5n with one single passage through each equipment. The advantage
of this arrangement option is; that it enables the elimination of the thickening stage 6, homogenization 7 and filtering 8 which is required in the conventional pelletizing process by ball mill wet grinding.
Figures 5 to 9 show the block diagrams of the tests that have been performed on the variation of arrangements provided in the conventional pelletizing process in which was included at least the crushing 5 which has been arranged along a pilot plant for the pelletizing process in accordance with the arrangements illustrated in Figures 1 to 4a. This pilot plant is provided with roller presses 5, ball mills 2 and 2a, hydrocyclones 4a, dryer 3, thickener 6, homogenizing tank 7, vacuum rotating filter 8, mixer, pelletizing disk 9 and a pilot furnace 10 for firing the iron ore pellets. The operating productivity of the set of comminution operation was measured for each test.
The quality characteristics of the raw and fired pellets produced during the various tests were evaluated in adequately chemical and physical laboratory for performing pelleting tests.
To evaluate the process with a pre-comminution 5 stage for the iron ore fines in the roller press followed by the supplementary conventional grinding in a ball mill as illustrated in Figure 2, three tests were performed with different materials. Two under wet grinding as illustrated in Figure 5 and one dry grinding as shown in the diagram of Figure 6. The results of these tests have ascertained that the pre-comminution 5 of the fines in a roller press in combination of a supplementary grinding operation in a
congenital ball mill produced raw and fired pellets of satisfactory quality and the increasing in the operating productivity ranged 20 to 33%.
For the ore fines post-comminution 5 in a roller press after the conventional grinding in ball mills as illustrated in Figure 3, three tests were performed with different materials. Two with wet grinding shown in the diagram of the Figure 7 and one with dry grinding as illustrated in the diagram of the Figure 8. The results of these test have indicated that the iron ore fines grinding in a ball mill up to a coarser granulometry than that obtained with the conventional process in combination with post-comminution 5 via the passage of the pre-ground material through a roller press, it can also be achieved satisfactory quality indices of the processed products. These tests have shown an expressive increase in the operating productivity, between 20 and 36%.
For ore fines comminution circuits 5, 5a,...,5n through successive passages in roller presses as illustrated in Figures 4 and 4a, three tests were performed with different materials as can be seen in Figure 9. In each one the material was submitted to a determined number of passages through the recalculating by the roller press 5 until the material reached the desired specific surface. Also, in these tests were obtained results that has shown good quality indices for the raw and fired pellets obtained from successively crushed iron ore fines. The gain in productivity reached in these tests was 26 to 30%.
Therefore, it is possible to conclude that the introduction of roller press
equipment in the pelletizing process according to one of the proposed arrangements, Figures 2, 3 and 4, afford a considerable increase to the process productivity in the yield of raw or fired pellets at the rate that a portion of the iron ore fines comminution operation 5 is no longer being executed in the conventional ball mills.
In spite of the description and illustrations above be related to a preferred embodiment of the present invention, it is to be understood that changes is possible without any deviations from the scope of the invention.
1. A process for producing iron ore pellets comprising the steps of providing one or
more roller press in the process and subjecting iron ore to crushing in said roller
press to comminute the iron ore for production of iron ore pellets.
2. The process of claim 1 optionally comprising a step of grinding the iron ore, said
grinding step including at least one of grinding and/or wet grinding and/or open
grinding and/or closed grinding wherein the crushing step is performed
independently from said grinding step.
3. The process of claim 2, wherein raw material to be pelletized is fed to said roller
press defining a pre-comminution stage of said material and submitting the pre-
comminuted material to other said grinding step in ball mills.
4. The process of claim 3, wherein the iron ore fines for pelletizing are submitted to
ore single passage through said roller press resulting in an increase of a
specific surface from approximately 450 cm2/g to about 1800 cm2/g to obtain a
crushed material and feeding the crushed material to [the] a conventional
grinding ball mill circuit in which the specific surface is increased to about 1800
5. Process as claimed in anyone of the preceding claims wherein a material
comminution in said crushing step for palletizing is processed of the said grinding
step performed in a ball mill.
6 The process of claim 5, wherein iron ore fires have a specific surface increased from approximately 450 cm2/g to about 1400 cm2/g in a wet grinding ball mill.
7. The process of claim 6, wherein at a wet grinding step the ground product is
submitted to stages of thickening, homogenizing and filtering, followed by
said crushing step of the filtered material by passing same only once
through the roller press until the specific surface reaches 1800 cm2/g.
8. The process of claim 6, wherein at a dry grinding step the ground product
with about a specific surface of 1400 cm2/g is submitted to a single passage
through the roller press resulting in a material with a specific surface of
approximately 1800 cm2/g.
9. The process of claim 1, comprising a total communication of the material to
be pellctized is provided in said crushing step and wherein iron ore fines
having a specific surface increased from approximately 450 cm2/g are
produced in said crushing step by successive passages of the material
through a plurality of roller presses.
10. The process of claim 1, wherein a sequence of "n" crushing steps in series are preformed with ore single passage of the material through equipment.
The present invention concerns a process for production of iron ore pellets comprising at least one iron ore crushing stage in a roller press for the production of iron ore pellets. The crushing stage (s) can be done prior or after grinding, or still defined by successive passages of the material through the foregoing crushing stage.
|Indian Patent Application Number||02224/CAL/1997|
|PG Journal Number||32/2007|
|Date of Filing||25-Nov-1997|
|Name of Patentee||COMPANHIA VALE DO RIO DOCE|
|Applicant Address||BRAZILIAN CORPORATION,BR-262-KM 296,SANTA LUZIA,MINAS GERAIS,BRAZIL|
|PCT International Classification Number||B02C 4/02|
|PCT International Application Number||N/A|
|PCT International Filing date|